An essential step in the retroviral life cycle is the integration of a DNA copy of the virus into the host genome. This integration is catalyzed by the virus-encoded integrase, IN. The IN protein is an attractive target for anti-retroviral drug therapy both because IN is essential for viral propagation and because IN homologs probably play no role important to the health or survival of the host cell. The rational design of anti-IN drugs depends upon the knowledge of the structure of IN. The overall goal of this project is to facilitate solution of the X-ray crystal structure of the IN protein encoded by the HIV retrovirus, the etiological agent of Acquired Immunodeficiency Syndrome (AIDS). We believe that a focussed, concentrated effort to maximize production of soluble forms of IN will prove to be the most efficient way to facilitate its crystallography. Because even small and subtle changes in amino acid sequence can have profound effects on the solubility of a protein and on one's ability to crystalize it, the IN proteins encoded by both HIV-1 and HIV-2 will be investigated. Overproduction and solubility of native IN will be systematically studied using the bacteriophage T7 expression system. In addition we will construct expression systems for the reverse transcriptase-IN fusion protein from which IN is proteolytically cleaved in vivo, and for fusion proteins with the maltose binding protein (MBP) and glutathione-S-transferase (GST) both of which have been found to enhance solubility of foreign proteins overexpressed in E. coli. Expression levels, product solubility and enzymatic activities will be characterized. Partial proteolysis of IN will be used to define protein domains, stable proteolytic fragments will be characterized and genes for their expression will be constructed.